The purpose of this proposal is to use photosynthetic mutants and viral infection as probes to study the nature of optical phemomena that reflect the high-energy state and conformational changes in photosynthetic membranes. We shall attempt to isolate temperature sensitive mutants of blue-green algae that are defective in Photosystem II. These will be selected for by changes in their fluorescent properties and in their O2 evolving characteristics. We will then compare fluorescence and delayed light data from wild-type cells with that obtained from mutant cells. We will also use both intrinsic (chlorophyll fluorescence) and extrinsic (ANS fluorescence) probes to measure the effect of viral infection on membrane conformation. We plan next to study fluorescence and delayed light phenomena under specific conditions to determine if they can be used as semi-quantitative assays for proton uptake or membrane potential, respectively. It is felt that this approach will yield new types of information of the conformational changes that occur in these membranes, and may aid in understanding the molecular interactions that take place in a highly functional membrane.